Cycloolefins, in particular, cyclohexene compounds are valuable as intermediates of organic chemical industrial products, and are particularly useful as a starting material for polyamides and lysine.
On the other hand, cycloalkanes, in particular, cyclohexane compounds are industrially useful as an organic chemical product, particularly, as a starting material of caprolactam, adipic acid, etc. and as an organic solvent.
Various methods of producing cycloolefins are known. The most common method is a method of partially hydrogenating a monocyclic aromatic hydrocarbon using a ruthenium catalyst. In this method, an appreciable amount of cycloalkane, which is a completely hydrogenated product and a useful industrial starting material, is necessarily by-produced. Therefore, this method is substantially a method of producing a cycloolefin and a cycloalkane concurrently.
As a means for improving the selectivity and yield of cycloolefin, many results of examinations made for catalyst components, and kinds of carriers and metal salts as additives to reaction systems have been reported. Of these, as to the reaction system in which water and zinc coexist, which shows a relatively high molar ratio of cycloolefin formed, i.e., a relatively high selectivity of cycloolefin, the following methods are proposed for example.
(1) A method for partially reducing a monocyclic aromatic hydrocarbon with hydrogen in the presence of water and at least one kind of zinc compound under a neutral or acidic condition, using a particulate hydrogenating catalyst mainly comprising metallic ruthenium having an average crystallite size of 200 .ANG. or less (JP-B-8-25919 (the term "JP-B" as used herein means an "examined Japanese patent publication") and U.S. Pat. No. 4,734,536). PA1 (2) A method for producing a cycloolefin by partially hydrogenating a monocyclic aromatic hydrocarbon in the presence of a ruthenium catalyst, in which at least one of a zinc oxide and a zinc hydroxide at an amount of not more than saturation solubility is present in the reaction system in a completely dissolved state (JP-B-5-12331). PA1 (3) A method for partially reducing a monocyclic aromatic hydrocarbon with hydrogen in the presence of water, in which a reaction is conducted using hydrogenated catalyst particles comprising metallic ruthenium having an average crystallite size of 200 .ANG. or less as a main component in the presence of at least one kind of a solid basic zinc under a neutral or acidic condition (JP-B-8-19012). PA1 (1) Among the methods of producing a cycloolefin using a ruthenium catalyst, the proposed methods for performing the reaction under alkaline conditions provide a lower formation ratio of a cycloolefin product, as compared with the methods where the reaction is performed under acidic conditions in the presence of zinc sulfate and water. Accordingly, when the formation ratio of a cycloolefin is desired to be controlled within higher ranges, the controllable range is disadvantageously narrow even if the reaction temperature and reaction pressure are changed. PA1 (2) On the other hand, with regard to the proposed methods of producing a cycloolefin under acidic conditions using zinc sulfate, water and a ruthenium catalyst, neither a specific controlling method of the formation ratio of the product nor a concept thereof has been suggested. Thus, for these methods, there has been no effective proposal for controlling the product formation ratio, which is required to be adjusted or changed in the case where the performance of the catalyst is changed or where some external disturbance happens and affects the reaction system, after starting the production. PA1 (3) The product formation ratio can be controlled by the changing the reaction temperature. However, the change of the reaction temperature is accompanied by a large load fluctuation on the facilities to remove or recover the reaction heat. Therefore, control by only changing the reaction temperature is not a preferred controlling means. PA1 (4) The product formation ratio can be controlled by varying the conversion rate of a starting material through characteristics of the reaction in the production method of a cycloolefin and a cycloalkane using a ruthenium catalyst, i.e., varying characteristics such that the higher the conversion rate of the starting material, the lower the formation ratio of cycloolefin formed, and the higher the formation ratio of cycloalkane instead. However, in this method, the concentration of the unreacted starting material contained in the product taken out from the reaction vessel fluctuates largely, and the load fluctuation in the step of separating the unreacted starting material is large. In particular, when a continuous reaction system of continuously feeding the starting material and continuously taking out the product is used, a large intermediate drum to absorb such fluctuation is required between the production facility and the subsequent separating and recovering step of the unreacted starting material, which is thus problematic and not preferred. PA1 (1) A method for producing a cycloolefin and a cycloalkane, which method comprises: PA1 a step of hydrogenating a monocyclic aromatic hydrocarbon under an acidic condition in the presence of a catalyst composition, PA1 (i) wherein said catalyst composition is a slurry which comprises a ruthenium catalyst, water and zinc sulfate, and which is preserved, prior to being used in said hydrogenation reaction, under a high temperature and high pressure hydrogen atmosphere of from 100 to 200.degree. C. and from 1 to 100 atm for 1 hour or more, and PA1 (ii) wherein said hydrogenation reaction is conducted under a controlled pressure, while maintaining a phase separated state of: PA1 (2) The method according to the above (1), wherein said hydrogenation reaction is conducted without changing a conversion rate of said monocyclic aromatic hydrocarbon. PA1 (3) The method according to the above (1) or (2), wherein the reaction temperature of said hydrogenation reaction is from 100.degree. C. to 200.degree. C. PA1 (4) The method according to the above (1), wherein said water phase has a zinc sulfate concentration of from 0.01 to 10 mol/liter. PA1 (5) The method according to any one of the above (1) to (4), wherein the weight of said water phase is from 0.001 to 100 times the weight of said monocyclic aromatic hydrocarbon. PA1 (6) The method according to any one of the above (1) to (5), wherein said ruthenium catalyst is a non-supported catalyst mainly comprising metallic ruthenium having an average crystallite size of 200 .ANG. or less, said metallic ruthenium being obtained by reducing a ruthenium compound. PA1 (7) The method according to the above (6), wherein said metallic ruthenium further contains a zinc compound, which is obtained by reducing a ruthenium compound containing a zinc compound, said metallic ruthenium having a zinc content of from 0.1 to 50% by weight based on the weight of ruthenium.
Further, the influence of the reaction temperature and reaction pressure on the reaction result has been extensively studied. It is already well known that when the water phase in the reaction system shows an alkaline condition or when a ruthenium chloride is directly reduced in the reaction vessel and starting material is put in the reaction vessel to undergo reaction, an increase of the reaction temperature and reaction pressure results in the increase of the yield of cycloolefin produced (J. Chem. Tech. Biotechnol., 1980, 30, 677-687, etc.).
On the other hand, in the method of hydrogenating a monocyclic aromatic hydrocarbon using a ruthenium catalyst in the presence of water and zinc sulfate in an acidic condition with zinc sulfate being dissolved in water, the reaction pressure hardly has an influence on the initial formation ratio of the product, i.e., the product formation ratio at the starting material conversion ratio of around 0 mol % (Applied Catalysis A: General, 83 (1992) 263-295), which is knowledge generally accepted in the art and there have been no data contrary thereto. According to this thesis, the product formation ratio and the adsorbed amount of hydrogen onto the surface of the catalyst correlate to each other, and the product formation ratio does not change as long as the adsorbed amount of hydrogen does not change, even if the hydrogen pressure in the reaction vessel is changed. The thesis concludes that when the hydrogen pressure in the reaction vessel is increased, the consumption rate of the adsorbed hydrogen on the surface of the catalyst becomes fast because the conversion rate of the starting material becomes fast. As a result, the adsorbed amount of hydrogen on the surface of the catalyst hardly changes, therefore, the initial formation ratio of the product is hardly changed. As is easily presumed from the above knowledge, with a reaction system in which at least a ruthenium catalyst, zinc sulfate and water coexist, the product formation ratio cannot be controlled by changing gaseous phase hydrogen pressure in the reaction vessel, which is substantially the reaction pressure.
In the method of producing a cycloolefin by partially hydrogenating a monocyclic aromatic hydrocarbon using a ruthenium catalyst, cycloalkanes which are completely hydrogenated products are necessarily by-produced in addition to cycloolefins which are partially hydrogenated products, as described above. Cycloalkanes are useful industrial products which compare favorably with cycloolefins. Accordingly, upon performing this method industrially, the need to control or change the formation ratio of a cycloolefin and a cycloalkane arises in accordance with the fluctuation in demand of a cycloolefin and a cycloalkane. If the formation ratio cannot be controlled, disposition of the overproduced material or a big storage tank are required. Alternatively, production should be done with an adjusting of the scale to that of the smaller demanded material. This leads to a decrease in operation rate of the production facility.
That is, in the method of producing a cycloolefin by partially hydrogenating a monocyclic aromatic hydrocarbon using a ruthenium catalyst, if the formation ratio of a cycloolefin and a cycloalkane to be produced cannot be controlled, such a producing method is industrially extremely inefficient.
Furthermore, the stability of the catalyst and/or reaction system does not reach an industrially satisfactory level in conventional producing methods. Therefore, in the case where the production is continuously performed, the formation ratio of a cycloolefin and a cycloalkane can fluctuate even under almost identical reaction temperature and reaction pressure conditions, which cause a further need of adjustment.
Therefore, for industrially performing the production of a cycloolefin using ruthenium, controlling methods to adjust or change the formation ratio of the product are essential. However, there have been the following four problems in conventional methods.